As electronic devices have been moving to higher-frequency operation, capacitors used in such devices as an electronic component, have been required to have excellent impedance characteristics at higher frequencies than before. In order to meet this requirement, various solid electrolytic capacitors with solid electrolytes made of conductive polymers with high electric conductivity have been suggested.
In recent years, solid electrolytic capacitors used in devices including CPU peripheries of personal computers are strongly desired to have smaller sizes and higher capacitances. In addition, such capacitors are required to have lower equivalent series resistance (ESR) for adaptation of high frequency, and to have lower equivalent series inductance (ESL) that is advantageous to denoising and transient response performance.
FIG. 15 is a perspective view of conventional solid electrolytic capacitor 501 described in Patent Literature 1. FIG. 16 is a plan view of capacitor element 21 of solid electrolytic capacitor 501. Capacitor element 21 includes: an electrode foil which serves as an anode body made of an aluminum foil, i.e., a valve metal; and a dielectric oxide film disposed on the surface of the electrode foil. The surface of the electrode foil is roughened. The electrode foil is separated into anode electrode portion 23 and a cathode forming area by insulating resist layer 22 disposed on the dielectric oxide film. Capacitor element 21 further includes: a solid electrolyte layer made of a conductive polymer disposed on the dielectric oxide film in the cathode forming area of the electrode foil; and a cathode layer disposed on the solid electrolyte layer. The cathode layer is composed of a carbon layer disposed on the solid electrolyte layer and a silver paste layer disposed on the carbon layer. The solid electrolyte layer and the cathode layer constitute cathode electrode portion 24. The electrode foil has a rectangular shape extending in a longitudinal direction. Capacitor element 21 has a planar shape. Anode electrode portion 23 and cathode electrode portion 24 are arranged in the longitudinal direction with resist layer 22 interposed between anode electrode portion 23 and cathode electrode portion 24.
Anode common terminal 25 is coupled with anode electrode portion 23 of capacitor element 21. A plurality of capacitor elements 21 are stacked one on another on anode common terminal 25, and anode electrode portions 23 of the plurality of capacitor elements 21 are joined together by a joining method, such as laser welding.
Cathode common terminal 26 is coupled with cathode electrode portion 24 of capacitor element 21. Bent portion 26A is formed by bending upward both sides of an element-mounting portion of cathode common terminal 26. The element-mounting portion of cathode common terminal 26 is joined with cathode electrode portions 24 of the plurality of capacitor elements 21 to electrically connect therebetween with a conductive adhesive. Cathode electrode portions 24 of the plurality of capacitor elements 21 are joined with one another to be electrically connected with the conductive adhesive. Bent portion 26A is joined with cathode electrode portion 24 to be electrically connected with conductive adhesive 27.
Insulating package resin 28 covers the plurality of capacitor elements 21 integrally with both a portion of anode common terminal 25 and a portion of cathode common terminal 26 being exposed to the outside surface. The portions of anode common terminal 25 and cathode common terminal 26 exposed from package resin 28 are bent along package resin 28 to a bottom of package resin 28, thus constituting surface-mounted solid electrolytic capacitor 501 with both an anode terminal portion and a cathode terminal portion formed on the bottom surface thereof.
In conventional solid electrolytic capacitor 501, the surface of the electrode foil made of the aluminum foil of capacitor element 21 is roughened by etching in order to increase the surface area per unit area thereof to increase the capacitance. Since the etching technology and mechanical strength of aluminum foils limits a further increase in the surface area, it appears to be difficult to obtain higher capacitance beyond the limitation.